The instant invention provides a novel route for producing bis-(N,N-dialkylamino)alkyl ethers. More particularly, the present invention provides a process for producing bis-(N,N-dialkylamino)alkyl ethers by the direct catalytic reaction of (N,N-dialkylamino)alkanol.
Bis[beta(N,N-dimethylamino)alkyl]ethers, including the commercially important bis[2-(N,N-dimethylamino)ethyl]ether ("BDMEE"), are known to be valuable polyurethane catalysts, particularly in the production of flexible polyurethane foam. By way of illustration, the production of polyurethane foam by reacting an organic isocyanate with an active hydrogen-containing compound (polyol) in the presence of a bis[beta(N,N-dimethylamino)alkyl]ether catalyst is disclosed in U.S. Pat. No. 3,330,782.
Several processes for the production of bis[beta(N,N-dimethylamino)ethyl]ethers, including BDMEE, are known. One process which utilizes di(2-chloroethyl) ether as a reactant is disclosed in U.S. Pat. Nos. 3,400,157 and 3,426,072. However, there are several disadvantages associated with the use of di(2-chloroethyl) ether, including (a) the need to employ comparatively expensive corrosion resistant equipment because of the presence of chlorides in the reaction mixture, (b) disposal problems associated with by-product chlorides, and (c) the relatively high cost and lack of readily available di(2-chloroethyl) ether. Another process for the production of bis[beta(N,N-dimethylamino)alkyl]ethers involves reacting a beta(N,N-dimethylamino) alkanol, a beta(N,N-di-methylamino) alkyl chloride, and an alkali metal hydroxide using a modified Williamson synthesis as disclosed in U.S. Pat. No. 3,480,675. However, this modified Williamson synthesis has several disadvantages including (a) several solids handling steps, (b) a discontinuous mode of operation, (c) disposal problems associated with by-product sodium chloride, and (d) one of the reactants, 2-dimethyl-aminoethyl chloride, used in the production of BDMEE is an unstable liquid and is also a vesicant which requires special handling. A further process for the production of BDMEE which comprises reacting trimethylamine with 2-[2-(N,N-dimethylamino)ethoxy]ethanol in the presence of a nickel catalyst under superatmospheric pressure is disclosed in U.S. Pat. No. 3,957,875. However, this process requires the use of a costly high-pressure reactor and provides product yields that leave room for improvement. Accordingly, it is desirable to provide a process for the production of bis(N,N-dialkylamino)alkyl ethers including BDMEE, that does not possess the disadvantages associated with the above-mentioned processes.
Two recent patents have sought to provide a more satisfactory process for preparing bis-(N,N-dialkylamino)alkyl ethers without the aforesaid disadvantages. In U.S. Pat. No. 4,177,212 a two-step, one pot, reaction is described that reacts a sodio N,N-dialkylaminoalkoxide with a sulfur oxychloro-containing compound in the presence of an organic diluent and an N,N-dialkylaminoalkanol to produce an intermediate and thereafter heating the intermediate to elevated temperatures to produce the bis-(N,N-dialkylamino)alkyl ether. U.S. Pat. No. 4,247,482 is also a two-step, one pot, process that utilizes SO.sub.3 vapor and sodio N,N-dialkylaminoalkoxide to provide an intermediate which is likewise heated at elevated temperatures to obtain the bis(N,N-dialkylamino)alkyl ether. Although these patents avoid many of the problems associated with the prior art, there continues to exist a need for processes that are simpler to operate and more economic to run.
The present invention is believed to provide these advantages through the direct reaction of alkanolamines over acid catalysts. Practical syntheses of bis-aminoalkyl ethers directly from alkanolamines are conspicuously absent from the literature.
The amine function complicates the direct acid-catalyzed synthesis since it provides an alternate reaction pathway which does not lead to ethers. For example, over a solid acid, amines may bind strongly at the acid sites and thus inhibit formation of alkoxide which reacts further to the ether. In fact, blockage of Lewis sites on alumina with pyridine nearly eliminates formation of diethylether from ethanol. The relative basicity of nitrogen and oxygen then governs the relative rates for each pathway. Unfortunately, because nitrogen is more basic than oxygen, reaction will occur preferentially at the amine. Thus, the direct etherification is not favored. Any hope of success then rests on some reversibility of the amine adsorption at the acid site, some equilibrium which would allow for hydroxyl attack, or an entirely different mechanism.
Thus, the present invention is indeed a novel and unexpected advance in the art.